Spatial modelling of Bacillus anthracis ecological niche in Zimbabwe.

Anthrax continues to cause significant mortalities in livestock, wildlife and humans worldwide. In Zimbabwe, anthrax outbreaks have been reported almost annually over the past four decades. In this study we tested whether anthrax outbreak data and a set of environmental variables can be used to predict the ecological niche for Bacillus anthracis using maximum entropy modelling for species geographical distribution (Maxent). Confirmed geo-referenced anthrax outbreaks data for the period 1995-2010 were used as presence locations and a set of environmental parameters; precipitation, temperature, vegetation biomass, soil type and terrain as predictor variables. Results showed that the environmental variables can adequately predict the ecological niche of B. anthracis (AUC for test data=0.717, p<0.001), with soil type as the most important predictor followed by variance of vegetation biomass and maximum temperature. These results imply that the model we tested may be used by animal health authorities in devising better control strategies for anthrax.

Awareness and attitude toward zoonoses with particular reference to anthrax among cattle owners in selected rural communities of Zimbabwe.

We conducted a cross-sectional study to assess cattle owners' awareness, perceptions, and attitudes toward zoonoses, with particular emphasis regarding anthrax. Data on awareness of zoonoses, clinical signs of anthrax in animals and human, its routes of transmission and methods of prevention, the families' consumption habits of anthrax-infected carcasses, and other family activities that increase exposure to anthrax were collected using an interviewer-administered questionnaire. A total of 41.4% (135/326) of the farmers were from high-anthrax-risk districts, whereas 28.5% and 30.1% were from medium- and low-risk districts, respectively. Overall, the level of awareness amongst the farmers for the named zoonoses were rabies (88.7%), anthrax (71.5%), and brucellosis (20.9%). Except for anthrax, awareness of other zoonoses did not differ significantly (p>0.05) among the district categories. Farmers from anthrax high-risk districts were significantly more aware of anthrax compared to those from moderate- (p=0.000) and low- (p=0.000) risk districts. All of the farmers were aware that anthrax occurs in cattle, and 73% indicated the presence of unclotting blood oozing from natural orifices as a consistent finding in cattle that died of anthrax, whereas 86.7% of them indicated the presence of skin lesions as the most common sign of the disease in humans. The good efficacy of human anthrax treatment (58.3%), slaughter of moribund cattle and selling of meat from cattle found dead to unsuspecting consumers (59.8%), reluctance to lose animals (47.9%), and forgetting about anthrax (41.1%) were cited as the major reasons for consuming anthrax-infected carcasses. Given that 75.2% of cattle owners indicated that they would not consume meat from cattle found dead, because they were discouraged by veterinary authorities, introducing meat inspection services is likely to have a positive impact in preventing human anthrax outbreaks in Zimbabwe.

Isolation of Bacillus anthracis from soil in selected high-risk areas of Zimbabwe.

AIMS: To isolate Bacillus anthracis from cattle carcass burial sites from high-risk districts in Zimbabwe. METHODS AND RESULTS: Soil samples were collected from carcass burial sites from seven areas, including two national game parks. Samples were collected from top 5-10 cm, and for spore extraction, 25 g of soil was suspended in sterile distilled water overnight. Supernatants were filtered through 0.45-µm pore cellulose nitrate, deposits suspended in 5 ml phosphate-buffered saline, aliquoted and heated at temperature regimen of 65, 70, 75 and 80 °C for 15 min. Samples were plated onto PLET agar. B. anthracis isolates were identified using growth morphology and PCR detecting pXO1 and pXO2 virulence plasmids. From samples heated at 75 °C for 15 min, B. anthracis were isolated from 9 of 81 (11.1%) soil samples representing five of the seven sampled areas. CONCLUSIONS: We isolated B. anthracis from soil collected from carcass burial sites. PCR targeting virulence plasmids provided a rapid confirmation of B. anthracis. SIGNIFICANCE AND IMPACT OF THE STUDY: The positive isolation indicated that some carcass burial sites may retain viable spores for at least 12 months after the previous outbreak, which suggests that they may be important sources of B. anthracis and new disease outbreaks.